1. Field of the Invention
The present invention relates to a method for configuring a data transmission interface in a communication network adopting a transmission protocol for transmission of data in units of grouped data.
2. Description of the Prior Art
Typically, a communication network comprises a core network which is independent of the connection technology used and handles “administrative” topics occurring in the network, as well as an access network. The access network is in charge of enabling terminals to access the communication network for communicating via the network with other terminals. The access network is dependent on the technology used for establishing connection with terminals (for example wireless or non-wireless connection).
For explanatory purposes only, the present description focuses on a wireless access network which is commonly referred to as radio access network (RAN), which enables terminals to access the network via an air-interface.
Thus, the radio access network RAN as referred to in the present description means a so-called 3rd generation RAN (3GRAN) conforming to the standards elaborated by the 3rd generation partnership project (3GPP).
Nevertheless, the principles as outlined in the present invention are intended to be understood in its broadest sense. Therefore, the communication network described in the present description is intended to mean any communication network, whether for mobile or non-mobile communication, as long as the communication network utilizes a packet or cell switched transmission protocol, that is a transmission protocol for transmission of data in units of grouped data. Examples for such transmission protocols are the Asynchronous Transmission Mode (ATM) protocol or the Internet Protocol (IP). ATM may be used in connection with an access network or base station subsystem (BSS) operated on the basis of Wideband Code Divisional Multiple Access WCDMA, while IP may be used in connection with a base station subsystem (BSS) operated on the basis of WideBand Code Divisional Multiple Access WCDMA or operated fully on the basis of the IP protocol.
As regards the constitution and/or topology of the radio access network, a plurality of base stations BS (also referred to as Node_B) are provisioned as access nodes for establishing connection with terminals (mobile station MS or user equipment UE). The access nodes are in turn controlled by a radio network controller RNC (corresponding to a base station controller BSC in GSM systems).
The base stations BS are connected to the radio network controller RNC such that at least one access node (base station) is connected to the access network control node (radio network controller) by an intermediate of at least one further access node. There may also be access nodes that do not have any intermediate nodes, like BS1 and BS4, as shown in FIG. 2. Stated in other words, the base stations are provided in respective chains of typically two to five (or more) base stations, while a plurality of such chains may be connected in a star connection type to the radio network controller. Still further, within a chain of base stations, the chain may be branched to two or more branches. FIG. 2 shows an example for the topology of a radio access network RAN in which the base stations BS1 to BS6 are each provided with an ATM Cross Connect means AXC.
The interface via which the access nodes (base stations) communicate with the control node (radio network controller) is known as the Iub interface (corresponding to the Abis interface in GSM). Data transport via the Iub interface, however, is subject to delays and delay variations. A main objective in network design is the minimization of imposed delays and also the minimization of delay variations. The delays are typically caused due to network design particulars, and once a network topology has been chosen, the delays can not be altered any more. On the other hand, delay variations are often created by a mechanism that allows at least some trade-off between delay variation and network capacity utilization, i.e. the higher the capacity utilization is chosen, the higher delay variations are accepted, while the lower the capacity utilization is chosen, the smaller are the delay variations to be taken into account.
In connection with data transmission via the Iub interface, the Iub transport delay and delay variations are due to an accumulation of individual delays/delay variations originating from several components:
AAL2 (ATM Adaptation Layer type 2) shaping,
AAL2 multiplexing,
ATM multiplexing and switching and
transmission (via the physical transmission media).
Delay components as briefly introduced before are graphically represented in FIG. 1 for the case of a WCDMA transmission based base station subsystem BSS of the radio access network RAN. For a WCDMA based BSS, the delay components for transmission/transport include                AAL2 multiplexing,        ATM multiplexing        PDH/SDH multiplexing (Plesiochronous Digital Hierarchy/Synchronous Digital Hierarchy) and        the physical transmission media (such as the microwave radio, fibres, copper wires etc.).        
A total value of delay/delay variation between any base station BS and/or base transceiver station BTS and the radio network controller RNC is fixed and constant for every base station BS.
Now, with regard to FIG. 1, the delay components in a vertical column in the drawing representation correspond to an individual base station, while for a chained base station topology as shown in FIG. 2, the delays imposed on data transmission of individual columns are added for obtaining the overall delay. In this model, it has to be noted that for each base station BS connection to the RNC, only one AAL2 multiplexing delay is relevant, since the data need not be ATM adapted before reaching the RNC. Also, the dashed boxes in FIG. 1 indicate a non mandatory intermediate equipment operating up to and including the ATM layer.
Thus, FIG. 1 could be interpreted (when neglecting the dashed column in the middle) such that the left column represents base station BS4 in FIG. 2, while the right column represents the base station BS5 (or BS6) in FIG. 2.
Apparently, it can then be observed that the ATM switching delays and delay variations as well as the transmission delays heavily depend on the position of the respective base station in the topology of the transport and transmission network, which positions could qualitatively be characterized by the words “near” (for example BS4) or “far” (for example BS5 or BS6). This observation may be based on the model shown in FIG. 1 but also from the topology shown in FIG. 2, from which it becomes clear that BS1 being closer to the RNC than BS3 has inherently a lower transmission delay than BS3, and also that BS4 has inherently a lower transmission delay than BS5 (or BS6).
Just to give a numerical example, in such a topology ATM connections going up to the farthest base station are estimated to experience for example a 5 ms maximum delay or longer delay variations than ATM connections going to the nearest base station. Due to macrodiversity, however, the radio access network application can not make use of the maximum 5 ms delay advantage that the nearer base stations have over the farthest one, so the transport capacity utilization of the Iub interface is non-optimum.
The transport capacity utilization on the Iub interface, however, is rather crucial, since the Iub links requirements are often tight, especially when radio transmission is used (but also when wired transmission types are used). Thus, in existing scenarios, a capacity utilization of the Iub interface in the radio access networks is non-optimum.
A previous approach as proposed for standardization in the 3GPP is based on a fixed usage of the same fixed delay for AAL2/ATM delay for ATM packetization, multiplexing and depacketization on the Iub interface. The fixed value has been proposed to be 7 ms. Thus, with reference to FIG. 1, according to this proposal one source of additional delay variation has been removed by summarizing AAL2 multiplexing and ATM multiplexing blocks to a single delay component, while remaining delay variations (due to PDH/SDH multiplexing and/or used physical media) still adversely affect the capacity usage on the Iub interface.